The present invention relates to devices for transmitting torque between a shaft and a member mounted on the shaft, and, more particularly, to expandable devices for locking a centrally bored core type member to a shaft element.
Paper and plastic web materials utilized in industry for packaging, labeling, and other purposes are supplied in rolls that are wound upon tubular cores. When the rolls are being wound and unwound, the cores are mounted on shafts that are journalled in bearings and are either driven or restrained (by a braking arrangement) usually in a manner such that the web is under constant tension. Expanding devices commonly referred to as "air chucks" or "air shafts" are normally used to lock the core to the journalled shaft so that the web rolls rotate with the shaft as a unit. The term "air chuck" is normally used to designate a short device which is locked to a shaft by set screws and can be used alone to secure a narrow roll or can be used as one of a pair to secure a wide roll. In the latter instance, the chucks are spaced on the shaft so as to engage the ends of the core of the wide roll. The term "air shaft" normally is used to designate a longer device which is essentially an elongated air chuck constructed with an integral shaft. A shaft portion extends from each end of the air shaft. The "air shaft" is utilized for wide rolls, and, after the roll is slid thereon, the end shaft portions are positioned in the bearings which will support the roll.
The prior art air chucks and air shafts employ some form of double-walled annular inflatable bladder. In the simplest designs the bladders are doughnut-shaped and expand directly against the inner surface of the core. These designs are the least expensive and have the greatest torque transmitting ability since the entire surface of the bladder is in contact with the core. The bladder does not, however, provide a rigid driving connection between the shaft and core and cannot be used effectively with sensitive tension control equipment. In other designs, the bladders are positioned within cylindrical casings which have sections which move radially against the core when the bladder is inflated. The radially movable sections constitute a relatively small portion of the outer surface of the casing, therefore, only a fraction of the energy stored in the inflated bladder is used to grip the core and the torque transmitting capacity of these devices is limited. These designs are also fairly complex and tend to be relatively expensive to manufacture.